Experimental evidence supports the pro-inflammatory effect of Macrophage Migration Inhibitory Factor (MIF) in bladder inflammation, but how MIF mediates bladder inflammation is poorly understood. The long-term goal is to understand the mechanisms of MIF-mediated bladder inflammation with the aim of altering these processes to reduce or abolish bladder inflammation in patients with chronic painful conditions of the lower urinary tract. The overall objective of this proposal is to determine the contribution of specific urothelial receptors to MIF release and to MIF-mediated signaling and bladder inflammation. The central hypothesis is that there are two components to inflammation involving MIF: 1) increased release of MIF; and 2) upregulation of MIF receptors and subsequent increased signaling via MIF/receptor interactions that enhances and/or maintains inflammation. This hypothesis has been formulated based on preliminary data generated in the applicants' laboratory. The rationale for propos- ing these studies is that by increasing our understanding of signaling events both upstream and downstream of MIF in the bladder will identify potential therapeutic targets. The hypothesis will be tested by the following specific aims: 1) Determine the contribution of urothelial Protease Activated Receptors (PAR) to a novel mechanism of urothelial MIF release: Agonists with specificity for different PAR receptors will be used to induce MIF release from urothelial cells (both human, in vitro and in vivo, using mice) to determine which receptors are involved in MIF release. To determine the contribution of MIF to PAR-mediated bladder inflammation in vivo, bladder inflammation will be induced in mice by instilling specific PAR agonists while simultaneously antagonizing MIF. Physiological, histological and molecular changes in the bladder will be measured. 2) Identify the contribution of urothelial MIF receptors (CD74; CXCR4) to MIF signaling and cystitis: MIF receptor blockade will be used to examine changes in MIF-mediated signaling during a well-established model of cystitis (cyclophosphamide) in mice. These experiments will also determine the effect of MIF receptor blockade on mediating cystitis by measuring physiological, histological and molecular changes in the bladder. 3) Determine MIF and MIF receptor levels in clinical conditions with bladder inflammation: Urinary MIF levels will be determined in UTI, radiation cystitis and PBS/IC (Hunner ulcer vs non-Hunner ulcer) patients. MIF, CD74 and CXCR4 urothelial immunostaining will be examined in PBS/IC (Hunner ulcer vs non-Hunner ulcer) and MIF-mediated cytokine production in human detrusor smooth muscle cells from PBS/IC patients will be examined. This proposal is innovative because it focuses on MIF, a novel mediator of bladder inflammation. The pro- posed research is significant because a greater understanding of the mechanisms of MIF release during bladder inflammation and of the signaling pathways activated by MIF binding to urothelial MIF receptors is expected to result in the identification of novel therapeutic targets for inflammatory conditions of the lower urinary tract.